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period science definition
- A division of geologic time that is longer than an epoch and shorter than an era.
- The duration of one cycle of a regularly recurring action or event. See also cycle, frequency.
- An occurrence of menstruation.
- In the Periodic Table, any of the seven horizontal rows that contain elements arranged in order of increasing atomic number. All the elements in a particular period have the same number of electron shells in their atoms, equal to the number of the period. Thus, atoms of nickel, copper, and zinc, in period four, each have four electron shells. See Periodic Table.
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